1. Field of the Invention
The present invention relates to a drive device for driving light emitting diode elements, a light source device including such a drive circuit for light emitting diode elements, and a display including such a light source device.
2. Description of the Related Art
As a display, a liquid crystal display that employs a liquid crystal panel is widely prevalent. As is well known, the liquid crystal panel is not a self-luminous panel but displays images through modulation of white light emitted from a light source device referred to as a so-called backlight based on a video signal.
Currently, a cold cathode fluorescent lamp is widely employed as the light source of the liquid crystal display. However, in recent years, because of enhancement of the light emission efficiency of a light emitting diode (LED) element (hereinafter, referred to simply as “light emitting diode”), a liquid crystal display that employs light emitting diodes as its light source is also becoming known. The light emitting diode has the following advantages over the cold cathode fluorescent lamp: the light emitting diode is better for the environment because mercury is not used as its material; the light emitting diode can be driven by lower voltage; and the light emitting diode has more favorable temperature characteristics and response characteristics, and a longer lifetime. Therefore, it is expected that the light emitting diode light source will be widely prevalent in the further.
An invention relating to a light source device (lighting device) that employs light emitting diodes as a light source for a liquid crystal display as described above is disclosed in e.g. Japanese Patent Laid-open No. 2001-210122. This patent document (see FIG. 10) shows a configuration for driving light emitting diodes for light emission thereof. In this configuration, a constant current is applied from a power supply unit (DC-DC converter) to a series connection circuit (LED row) arising from series connection of plural light emitting diodes. Furthermore, a switch element formed of an FET is further connected in series to the series connection circuit of the light emitting diodes, and this switch element is turned on/off by a pulse width modulation (PWM) signal for dimming control of the LEDs.
As described above, a certain level of basic technical configuration for driving light emitting diodes as a light source has been increasingly common. However, when some sort of conditions typified by the driving system and various specifications for image displaying in an actual liquid crystal panel are taken into consideration, there still remains ample room for improvement in the performance and reliability of e.g. the configuration for driving light emitting diodes for light emission thereof.